Self-assembly is a term used to define the spontaneous association of entities into structural aggregates. The best-known and most well-researched area of self-assembly involves molecular self-assembly, that is, the spontaneous association of molecules, a successful strategy for the generation of large, structured molecular aggregates. Self-assembly of molecules in solution is described by Whitesides, et al., in “Noncovalent Synthesis: Using Physical-Organic Chemistry to Make Aggregates”, Accts. Chem. Res., 28, 37–44 (1995). See also Philp, et al., Angew. Chem., Int. Ed. Engl., 35, 1155–1196 (1996) for molecular self-assembly. Nature includes examples of molecular self-assembly where, in the field of biology, many processes involve interfacial interactions and shape selectivity to form complex, three-dimensional structures.
Self-assembly of molecules can be made to occur spontaneously at a liquid/solid interface to form a self-assembled monolayer of the molecules when the molecules have a shape that facilitates ordered stacking in the plane of the interface and each includes a chemical functionality that adheres to the surface or in another way promotes arrangement of the molecules with the functionality positioned adjacent the surface. U.S. Pat. No. 5,512,131 and U.S. patent application Ser. Nos. 08/659,537, 08/616,929, 08/676,951, and 08/677,309, and International Patent Publication No. WO 96/29629, all commonly-owned, describe a variety of techniques for arranging patterns of self-assembled monolayers at surfaces for a variety of purposes. See also Whitesides, G. M., “Self-Assembling Materials”, Scientific American, 273, 146–149 (1995) for a discussion of self-assembly.
Self-assembly of components larger than molecules is known, for example, self-assembly of bubbles at an air-liquid interface, small spheres self-assembled on surfaces, self-assembly of microspheres via biochemical attraction between the microspheres, and the like. Yamaki, et al., in “Size Dependent Separation of Colloidal Particles in Two-Dimensional Convective Self-Assembly” Langmuir, 11, 2975–2978 (1995), report “convective self-assembly” of colloidal particles ranging in size from 12 nm to 144 nm in diameter in a wetting liquid film on a mercury surface. Size-dependent two-dimensional convective assembly occurred, with larger particles being positioned in the center of the aggregate and smaller particles at the periphery. Cralchevski, et al., in “Capillary Forces Between Colloidal Particles” Langmuir, 10, 23–36 (1994), describe capillary interactions occurring between particles protruding from a liquid film due to the capillary rise of liquid along the surface of each particle. A theoretical treatment of capillary forces active spheres is presented. Simpson, et al., in “Bubble Raft Model for an Amorphous Alloy”, Nature, 237–322 (Jun. 9, 1972), describe preparation of a two-dimensional amorphous array of bubbles of two different sizes as a model of an amorphous metal alloy. The bubbles were held together by a general capillary attraction representative of the binding force of free electrons in the metal.
U.S. Pat. No. 5,545,291 (Smith) describes assembly of solid microstructures in an ordered manner onto a substrate through fluid transfer. The microstructures are shaped blocks that, when transferred in a fluid slurry poured onto the top surface of a substrate having recessed regions that match the shapes of the blocks, insert into the recessed regions via gravity. U.S. Pat. No. 5,355,577 (Cohn) describes a method of assembling discrete microelectronic or micro-mechanical devices by positioning the devices on a template, vibrating the template, and causing the devices to move into apertures. The shape of each aperture determines the number, orientation, and type of device that it traps.
While self-assembly at the molecular level is relatively well-developed, self-assembly at larger scales is not so well-developed. Many systems in science and technology require the assembly of components that are larger than molecules into assemblies, for example, microelectronic and microelectrochemical systems, sensors, and microanalytical and microsynthetic devices. Photolithography has been the principal technique used to make microstructures. Although enormously powerful, photolithography cannot easily be used to form non-planar and three-dimensional structures, it generates structures that are metastable, and it can be used only with a limited set of materials.
The fabrication of electronic devices is well established. Microelectronic devices are typically fabricated via photolithography, which is inherently a two-dimensional process. The three-dimensional interconnections required in state of the art microelectronics devices typically are fabricated by the superposition of stacked, parallel planes, and by their connection using perpendicular vias. While these arrangements have been very successful, they require numerous design considerations ranging from minimization of RC delays due to long interconnects, to dissipation of heat using cooling channels designed into three-dimensional structures.
U.S. Pat. No. 5,075,253 (Sliwa) suggests integration of segmented circuitry devices into two-dimensional arrangements using capillary forces at the surface of a floatation liquid.
Commonly owned, co-pending U.S. patent application Ser. No. 08/816,662, filed Mar. 13, 1997 by Bowden, et al., entitled “Self-Assembly of Macro Scale Articles”, as well as the following literature references: Bowden, et al. “Self-assembly of mesoscale objects into ordered two-dimensional arrays”, Science (Washington, D.C.) (1997), 276(5310), 233–235; Terfort, et al., “Three-dimensional self-assembly of millimeter-scale components”, Nature (London) (1997), 386(6621), 162–164; Bowden, et al., “Mesoscale Self-Assembly: Capillary Bonds and Negative Menisci”, J. Phys. Chem. B (2000), 104(12), 2714–2724; Bowden, et al., “Molecule-Mimetic Chemistry and Mesoscale Self-Assembly”, Acc. Chem. Res. (2001), 34(3), 231–238; Bowden, et al., “Self-Assembly of Microscale Objects at a Liquid/Liquid Interface through Lateral Capillary Forces”, Langmuir (2001), 17(5), 1757–1765, describe self-assembly of some electrical components, and self-assembly of some three-dimensional objects.
While the above and other arrangements are, in some cases, very promising, it would be desirable to introduce flexibility and variety into the possible techniques for fabricating three-dimensional circuitry.